Problem: In spherical coordinates, the point $\left( 3, \frac{2 \pi}{7}, \frac{8 \pi}{5} \right)$ is equivalent to what other point, in the standard spherical coordinate representation?  Enter your answer in the form $(\rho,\theta,\phi),$ where $\rho > 0,$ $0 \le \theta < 2 \pi,$ and $0 \le \phi \le \pi.$
Solution: To find the spherical coordinates of a point $P,$ we measure the angle that $\overline{OP}$ makes with the positive $x$-axis, which is $\theta,$ and the angle that $\overline{OP}$ makes with the positive $z$-axis, which is $\phi,$ where $O$ is the origin.

[asy]
import three;

size(250);
currentprojection = perspective(6,3,2);

triple sphericaltorectangular (real rho, real theta, real phi) {
  return ((rho*Sin(phi)*Cos(theta),rho*Sin(phi)*Sin(theta),rho*Cos(phi)));
}

triple O, P;

O = (0,0,0);
P = sphericaltorectangular(1,60,45);

draw(surface(O--P--(P.x,P.y,0)--cycle),gray(0.7),nolight);
draw(O--(1,0,0),Arrow3(6));
draw(O--(0,1,0),Arrow3(6));
draw(O--(0,0,1),Arrow3(6));
draw(O--P--(P.x,P.y,0)--cycle);
draw((0,0,0.5)..sphericaltorectangular(0.5,60,45/2)..sphericaltorectangular(0.5,60,45),Arrow3(6));
draw((0.4,0,0)..sphericaltorectangular(0.4,30,90)..sphericaltorectangular(0.4,60,90),Arrow3(6));

label("$x$", (1.1,0,0));
label("$y$", (0,1.1,0));
label("$z$", (0,0,1.1));
label("$\phi$", (0.2,0.25,0.6));
label("$\theta$", (0.5,0.25,0));
label("$P$", P, N);
[/asy]

The normal ranges for $\theta$ and $\phi$ are $0 \le \theta < 2 \pi$ and $0 \le \phi \le \pi.$  Since $\phi = \frac{8 \pi}{5}$ is greater than $\pi,$ we end up wrapping past the negative $z$-axis.  Thus, $\phi$ becomes $2 \pi - \frac{8 \pi}{5} = \frac{2 \pi}{5},$ and $\theta$ becomes $\frac{2 \pi}{7} + \pi = \frac{9 \pi}{7}.$  Thus, the standard spherical coordinates are $\boxed{\left( 3, \frac{9 \pi}{7}, \frac{2 \pi}{5} \right)}.$